Gel electrophoresis is commonly used to separate, by molecular size, biological molecules, such as deoxyribonucleic acid (“DNA”), ribonucleic acid (“RNA”) and proteins. To perform gel electrophoresis, a polymeric gel, such as polyacrylamide, is formed in a glass tube, or between spaced glass or plastic plates. The tube or plates are then placed in a container along with anode and cathode elements at the top and bottom of the gel. Sample wells formed in the top of the gel are first filled with buffer solutions. Molecule samples prepared in a sample buffer that may contain a tracking dye are then placed in the wells. Electrophoretic buffer solutions containing conductive ions are added to the container to make electrical contact between the gel, the samples in the wells and the anode and cathode elements. A voltage is then applied across the gel, which causes the sample molecules and any tracking dye to migrate toward the bottom of the gel, and separate into bands whose migration distance depends on molecular size.
For accurate electrophoretic separation, the first and second buffer solutions must be isolated from one another. To provide isolation, electrophoresis systems use various methods to hold the gel cassettes in contact with the buffer core and secure the buffer core assembly in the container. Previously known electrophoresis systems commonly use a buffer core subassembly containing clamps or latches that secure the gel cassettes to the buffer core.
Gel electrophoresis systems, such as the XCell SureLock™ Mini-Cell system manufactured by Invitrogen Corporation, of San Diego, Calif., or the electrophoresis system described in U.S. Pat. No. 6,001,233, include a container for receiving a first buffer solution and a buffer core assembly for receiving a second buffer solution. The buffer core assembly comprises a pair of gel cassettes affixed to front and back sides of a U-shaped buffer core body forming a buffer core assembly. The space defined by the upraised side members of the buffer core body and the end faces of the gel cassettes forms an upper buffer chamber. Once the cassettes are secured, the buffer core assembly is loaded in the electrophoresis container toward one end prior to electrophoretic separation. A cam-activated clamp is then inserted into an electrophoresis container near the other end, between the buffer core assembly and the back wall of the container. A cam on the cam-activated clamp is disposed to engage a back wall of the container to cause a mounting block to apply uniform pressure to secure the gel cassettes to the buffer core body. Since there is only one mounting block, this electrophoresis system is limited to one buffer core assembly with a maximum of two gel cassettes. If a second buffer core assembly is positioned on the cam side of the cam activated clamp, the cam may deform the gel cassette in contact with the cam, and this deformation of the gel cassette may allow leakage of the buffer solution from the upper buffer chamber in the second buffer core assembly.
In view of the practical limitations associated with prior art clamping methods and apparatus, it is desirable to provide a cam-activated lock that requires no clamping subassembly and is positioned between two buffer core assemblies to reliably secure electrophoresis gel cassettes in each of the buffer core assemblies. It is further desirable to provide a cam-activated lock that provides a consistent and reproducible clamping force each time the apparatus is used.
Another issue for users of gel electrophoresis apparatuses that can accommodate multiple buffer cores is the unnecessary use of large volumes of buffer when fewer than the maximum number of gels are run in the apparatus.
Furthermore, in certain aspects, provided herein is an apparatus for electrophoresis or electrophoretic transfer of biomolecules that that includes a buffer displacement dam in at least one buffer reservoir of the apparatus. The buffer displacement dam is a solid or partially or substantially hollow or open structure that conforms to the size of the interior of the buffer reservoir in at least one dimension, and replaces the space which would otherwise be occupied by buffer contained within the buffer reservoir during electrophoretic separation or transfer of biomolecules.